VENTRAL BODY CAVITY
The ventral body cavity is much larger than the dorsal one. It contains most of the soft organs (viscera) of the body. It is divided by the thin diaphragm muscle into the cranial thoracic cavity, also known as the thorax or chest, and the caudal abdominal cavity, also known as the abdomen.
Major structures in the thoracic cavity include the heart, lungs, esophagus, and many major blood vessels coming to and going from the heart. All of the organs in the thoracic cavity are covered by a thin membrane called the pleura. Even the cavity itself is lined by pleura. The layer that covers the organs is called the visceral layer of pleura because it lies right on the viscera (the organs). The layer that lines the whole thoracic cavity is called the parietal layer of pleura. The potential space between the two layers is filled with a small amount of lubricating fluid. The smooth pleural surfaces are lubricated by the pleural fluid to ensure that the two surfaces slide over each other easily during breathing. If the pleural surfaces become thickened and roughened by inflammation, a condition called pleuritis or pleurisy, the surfaces scrape over each other with each breath, making breathing very painful.
The abdomen contains the digestive, urinary, and reproductive organs. It is lined by a thin membrane called the peritoneum, which also covers its contents. The visceral layer of peritoneum covers the abdominal organs, and the parietal layer lines the abdominal cavity. As in the thorax, a potential space filled with peritoneal fluid separates the two layers. Inflammation of the peritoneum (peritonitis) is very painful and most commonly results either from a wound that penetrates into the abdomen from the outside or from a rupture or perforation of the GI tract. When performing surgery on the digestive tract, we must take care to suture it securely closed to prevent leakage, which could lead to peritonitis.
TEST YOURSELF 1-3
1. According to the principle of bilateral symmetry, single structures in the body are located on or near which anatomic plane of reference?
2. Where is the pleura found? Where is the peritoneum found?
3. What is the difference between the visceral and parietal layers of pleura and peritoneum?